First of all, it isn't the Gentoo way to install licenses in the doc directory, or indeed at all. Secondly, if the license file isn't installed in /usr/share/doc/opera/LICENSE, then the license agreement acceptance dialogue presented to the user at first launch shows an empty license field (bug #266280).
11.00_pre1029 now installs a single license.txt into </usr/share/opera/defaults/license.txt>, and symlinks to that directory are placed in any locale directories that had such a symlink to /usr/share/doc/opera/LICENSE.